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transparent gas upon the removal of the body it surrounds 

 to its second position nearer to the sun. But the atmo- 

 spheric condensation into cloud-like mist which follows the 

 removal of our little planet from the influence of the solar 

 rays would also result from the removal of those solar rays 

 from that little planet, such for instance as would be caused 

 by the interposition of one of the planets. Under these 

 circumstances a precipitation of misty material would take 

 place, a precipitation which would as before be dissipated at 

 the termination of the eclipse. 



A comet, however, is not circumstanced as our hypothe- 

 tical planet has been. It is not placed at some given 

 distance from the sun and allowed to remain there until 

 the maximum thermal efl'ect has been produced, and then 

 removed elsewhere. It is continually altering its distance 

 from the sun, and, apart from any axial rotation it may 

 have, is continually presenting a fresh aspect to the opera- 

 tion of the solar heat. Yapourised materials issue from its 

 heated surface in jets like steam, and rise towards the sun 

 into the cooler atmosphere above, where they lose a portion 

 of their heat, become partially condensed, and form a canopy 

 of cloud, which, when viewed from the side by the inhabi- 

 tants of another planet, presents the appearance of a 

 crescent with horns turned from the sun of a hemisphere or 

 a sphere of nebulous matter, according to the amount and 

 aggTegation of the misty particles. As the comet approaches 

 its perihelion this misty canopy is dissipated as transparent 

 gas into the upper and surrounding regions of its atmosphere 

 by the ever increasing power of the sun, whilst fresh jets of 

 steam arise from the heated surface of the central mass and 

 replenish the stratum of clouds. It is not diflicult to find 



